1. Field of the Invention
The present invention relates to a hybrid supercharging engine in which a supercharger having a power source other an exhaust gas is arranged in a supercharging system of an engine, particularly in a diesel engine (hereinafter referred to to as an xe2x80x9cenginexe2x80x9d), the system comprising a turbocharger and a supercharger in a series to the turbocharger, thereby supercharging the engine by two steps, and to an improvement of Japanese Patent Application No. 8-358847.
2. Description of the Related Art
A supercharging system using a turbocharger for the purpose of increasing the output of a diesel engine has been popular in Europe and America where a lot of flatlands are included; however, it has not been currently popular in Japan, where a lot of mountains and slopes are included, for the following reasons.
The turbocharger mentioned above is a speed type and has the characteristics shown in FIG. 2; however, there are the following disadvantages.
(a) When the turbocharger is mounted in a vehicle engine which requires a low speed torque in accordance with a characteristic of increasing a pressure ratio (hereinafter referred to as pressure) in proportion to a rotating speed and a flow amount in the turbocharger, it is possible to increase the torque, shown by a line c-d, at a time of no turbocharging, to a line a-b at a time of middle speed or more by setting the operation line to be line a-b in FIG. 2. However, the low speed torque is insufficient in comparison with a non-turbocharged engine, so that the starting and accelerating performance from a stop state (hereinafter referred to as zero starting performance) is particularly insufficient for a vehicle engine.
(b) Due to the characteristics of the turbocharger in a turbocharged engine, it is impossible to set not only the low speed torque but also the middle speed torque sufficiently higher than the high speed torque except by limiting the maximum engine output.
(c) In the item (a) mentioned above, the operation line a-b of the turbocharger in FIG. 2 only crosses the maximum efficiency curve c-d at a point r, so that the specific fuel consumption (hereinafter referred to as BSFC) is low near a point r in FIG. 3 corresponding to the r in FIG. 2. However, the efficiency of the turbocharger is low in engine operating states, other than this, and does not have a low BSFC.
(d) As a vehicle engine, the engine is operated along a running resistance curve f-b in FIG. 3, which illustrates the relationship of engine speed vs. BMEP, where BMEP is the engine torque divided by the supply air pressure ratio, so that the running specific fuel consumption of the vehicle, expressed by a unit of 1 km/1 in accordance with the BSFC in a g zone in FIG. 3 having the highest operating frequency, is widely affected. It has been known that the BSFC of the engine closes to an illustrated specific fuel consumption (hereinafter referred to as ISFC), shown by a chain line e-f, in correspondence to an increase of the BMEP, as shown in FIG. 5, and becomes low.
Explaining this by FIG. 3, the vehicle engine turbocharger operating along the line a-b in FIG. 3 increases the performance to the BMEP, for example, 16 kg/cm2, and the BSFC at that time can be set to be 140 g/ps-hr as shown by point a in FIG. 5. However, in the g zone of FIG. 3, the load of the engine becomes about a quarter and the BSFC at this time is increased to 200 g/ps-hr, shown by a point t in accordance with FIG. 5.
Accordingly, if the BMEP can be further increased to twice that of the turbocharger engine shown by a point j in FIG. 5, for example, 32 kg/cm2, the BSFC at a time of being applied a quarter load can be set to be 155 g/ps-hr, shown by a point I, from 200 g/ps-hr shown by the point t.
The current turbocharged engine should further increase the BMEP, and is desired not only to lower the BSFC thereby but also to make a further compact, light weight and inexpensive engine when the output is the same; however, it is impossible for the reasons mentioned above.
(e) A further reason preventing the turbocharged engine from being popular is turbo lag.
The speed of a turbocharger when the engine is in an idling state, at a time when the vehicle is stopped, is about 5000 rpm, and it is required that the turbocharger be accelerated to about 50,000 rpm when the vehicle accelerates. However, the turbocharger has no turbocharging function at the time of zero starting acceleration, so that the vehicle is forced to perform zero starting acceleration at the time of no turbocharging expressed by the line c-d in FIG. 3.
(f) The compression of the engine is increased by turbocharging, so that the maximum pressure at the time of combustion theoretically increases over the permitted maximum pressure of the engine. In a turbocharged engine a countermeasure is taken to meet this matter by reducing the compression ratio.
However, the compression ratio of a diesel engine is generally decided by taking the starting performance into consideration, so that a reduction of the compression ratio makes it hard to start the engine. A start assisting apparatus such as a glow plug or the like is useful for starting the engine, but is not useful for preventing the discharge of a white smoke containing virulent material, such as formaldehyde and the like, immediately after starting. Thus, at 100 rpm at the time of starting and at 600 rpm at the time of idling immediately after starting, the turbocharger does not function as a turbocharger, and does not increase the compressing pressure or the compressing temperature at the time of starting, so that the effect of such countermeasures on starting is a continuing problem.
The present invention is made for solving the problems mentioned above.
A first object of the present invention is to provide a hybrid supercharging engine having sufficient low speed torque, a high zero starting performance when mounted in a vehicle, being capable of obtaining a middle speed torque without sacrificing maximum output, having a small turbo lag, having a low specific fuel consumption and having an excellent starting performance.
A second object of the present invention is to provide a hybrid supercharging engine which can not only make it possible to set a low BSFC but also make it possible to obtain twice or more BMEP than a turbocharged engine.
A third object of the present invention is to provide a hybrid supercharging system for an engine which the increases the amount of air supplied to the engine by supercharging mainly by means of a supercharger at a time of a low speed, and which can obtain a performance at a time of a steady operation by accelerating a turbocharger, without generating a turbo lag even at at a time of a rapid acceleration from a low speed.
A fourth object of the present invention is to provide a hybrid supercharging system for an engine which effectively functions as a supercharger even at a time of starting, which increases the compression pressure and temperature of the engine and make it easy to start a high compression ratio engine which must be made to have a low compression ratio for starting.
A fifth object of the present invention is to provide a hybrid supercharging system for an engine which can make an engine compact, light weight and inexpensive, and can reduce exhaust Nox without sacrificing engine reliability.
A hybrid supercharging system for an engine, in accordance with the present invention, comprises a turbocharger which reaches its capacity at a speed higher than a maximum torque rotating speed of an engine, and a volume type supercharger provided in series to the turbocharger, wherein a two-step supercharging is performed while controlling the supercharger in such a manner as to keep a supply air amount constant without relation to the engine speed. Accordingly, the plurality of objects mentioned above can be achieved. Further, the present invention is characterized by adjusting the amount of air supplied by the volume type supercharger by a bypass valve in a bypass provided in the volume-type supercharger end and by a supply air flow meter provided in parallel to the valve. Alternatively, the bypass valve in the bypass provided in the volume-type supercharger end may be used with a rotating speed meter provided in the supercharger. Accordingly, the supply air amount can be accurately adjusted.
Still further, the present invention is characterized in that the hybrid supercharging system adjusts the maximum supply air pressure by a supply air pressure meter provided in the supply air system and a bypass valve in a bypass provided in the volume-type supercharger end, so that the pressure within a cylinder of the engine is not over an allowed maximum pressure of the engine. Accordingly, a maximum supply air pressure can be obtained within a range not over the allowed maximum pressure of the engine.
Furthermore, the present invention is characterized in that the hybrid supercharged engine is provided with a Miller cycle system which can obtain a high expansion ratio, and with system controls to reduce the compression ratio and maintain a low specific fuel consumption so that the pressure within the engine cylinders is not over the allowed maximum pressure of the engine. Accordingly, the compression ratio can be reduced, the allowed maximum output of the engine is restricted and the low specific fuel consumption can be obtained.
Moreover, the present invention is characterized by structuring the volume type supercharger in such a manner as to drive it through a slip clutch, controlling the clutch by the supply air pressure meter and the supply air flow meter so as to change the slip rate, and adjusting the supply air pressure and the supply air flow amount to the engine. Accordingly, it becomes easy to control the volume type supercharger.
Further, the present invention is characterized by structuring the volume type supercharger in such a manner as to drive it through a continuously variable transmission, controlling the transmission so as to change the rotating ratio between the engine and the volume type supercharger, and adjusting the supply air pressure and the supply air flow amount to the engine. Accordingly, it becomes easy to control the volume type supercharger.
Still further, the present invention is characterized by structuring the volume type supercharger in such a manner as to drive it through a differential gear mechanism, controlling the differential gear mechanism by the supply air pressure meter, the flow amount meter and the pressure adjusting valve, and adjusting the supply air pressure and the supply air flow amount to the engine. Accordingly, it becomes easy to control the volume type supercharger.
Furthermore, the present invention is characterized by structuring the volume type supercharger in such a manner as to drive it by a spark ignition engine, and controlling the spark ignition engine so as to perform an exhaust gas recirculation (an EGR), thereby reducing Nox. Accordingly, it becomes easy to control the volume type supercharger.
Moreover, the present invention is characterized in that the volume type supercharger is a speed type supercharger. Accordingly, the speed type supercharger can achieve the plurality of objects mentioned above, as in the case of the volume type supercharger.